Ptc device

ABSTRACT

A PTC device comprises a current and temperature sensing element, a first insulating layer, a second insulating layer, a first electrode layer and a second electrode layer. The current and temperature sensing device is a laminated structure comprising a first conductive layer, a second conductive layer and a PTC material layer. The first and second conductive layers are disposed on first and second surfaces of the PTC material layer, respectively. The second surface is opposite to the first surface. The first and second insulating layers are disposed on the first and second conductive layers, respectively. The first electrode layer is disposed on the first insulating layer and electrically connects to the first conductive layer. The second electrode layer is disposed on the second insulating layer and electrically connects to the second conductive layer. Corners of the current and temperature sensing device are provided with insulating members.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present application relates to a thermistor. More specifically, itrelates to a positive coefficient temperature (PTC) device.

(2) Description of the Related Art

A PTC device can be used for circuit protection to avoidover-temperature or over-current which would cause damages. A PTC deviceusually comprise two electrodes and a resistive material disposedtherebetween. The resistive material has PTC feature, i.e., it has anlow resistance at a normal temperature; however, when an over-current oran over-temperature occurs in the circuit, the resistanceinstantaneously increases to extremely high resistance (i.e., trip) todiminish the current for circuit protection. The PTC device can beapplied to temperature sensing circuit to sense ambient temperature, soas to determine on whether to take actions for over-temperatureprotection such as shutdown or power off. When the temperature decreasesto room temperature or over-current no longer exists, the over-currentprotection device returns to low resistance state so that the circuitoperates normally again. Because the PTC devices can be reused, they canreplace fuses or other temperature sensing devices to be widely appliedto high-density circuitries.

With lightweight and compact trends, electronic apparatuses are gettingsmaller. For a cell phone, a number of components have to be integratedinto a limited space, in which an over-current protection device isusually secured to a protective circuit module (PCM) and its externallead will occupy a certain space. Therefore, it is desirable to have athin-type protection device that does not take up much room. When thedevice is downsizing to form factor 0201, it is a great challenge on howto decrease the thickness of the protection device for surface-mountapplications.

According to specification of 0201, a device has a length of 0.6±0.03mm, a width of 0.3±0.03 mm and a thickness of 0.25±0.03 mm. Inmanufacturing, the length and width are doable, but the thickness is toothin to be achieved. Nowadays, the resistive material substrate ofcarbon black system can be at most pressed to 0.2 mm in thickness, andthe resistive material substrate of ceramic filler system can obtain athickness of 0.2-0.23 mm. If the resistive substrate is further engagedwith insulating (prepreg) layers and internal and external circuits(electrodes) to form an over-current protection device as shown in U.S.Pat. No. 6,377,467, not only is the thickness out of specification butalso the thickness may be equal to or larger than width. As a result,the devices may topple when they are subjected to packaging or otherprocesses afterwards. Moreover, the internal-and-external circuit designon a small size device sometimes has misalignment between the internalcircuit and external circuit, and therefore the production yield will benegatively impacted.

U.S. Pat. No. 9,007,166 proposes a solution to the aforesaid problem.Without prepreg layers and external electrode layers, a PTC compositesubstrate is devised to etch or cut an electrode layer of the PTCcomposite substrate to form a groove isolating right and leftelectrodes, so as to control the thickness of the PTC over-currentprotection device to be smaller than or equal to 0.28 mm. However, theelectrode layers of the PTC device are not symmetrical, and thereforethere is a need to verify the orientation of the PTC device underelectric testing and packaging. Moreover, the groove may be misaligneddue to inflation and retraction of the PTC material duringmanufacturing, and the right and left electrodes of unequal areasinfluence electric characteristics. Without support of prepreg layers,the PTC device may flaw due to insufficient strength duringmanufacturing. Moreover, the PTC material may be molten caused by hightemperature during cutting. During a first cut, e.g., along X-axis, themolten material is moved away by a cutter, burr or flash is not aserious problem. However, during a sequential second cut, e.g., alongY-axis, molten material residue may exist in the groove of the first cutto incur burr or flash. The burr problem is less serious for devices oflarge sizes and becomes more serious for devices of small sizes. Theburr incurs rough surfaces and uncontrollable dimensions of the deviceand therefore impacts sequential processes including tape and reel,surface mounting and soldering.

In view of the above, for downsizing PTC devices, it is a greatchallenge to diminish burr or flash after cutting to avoid thesequential tape and reel, SMT mounting and soldering processes.

SUMMARY OF THE INVENTION

The present application provides a PTC device characterized inover-current protection and/or over-temperature sensing. The PTC devicein which a current and temperature sensing element is provided withinsulating members at corners connecting to adjacent lateral surfaces isdevised to increase structural strength, avoid burr or flash, andimprove manufacturing yield.

In accordance with an embodiment of the present application, a PTCdevice comprises a current and temperature sensing element, a firstinsulating layer, a second insulating layer, a first electrode layer anda second electrode layer. The current and temperature sensing element isa laminated structure of a first electrically conductive layer, a secondelectrically conductive layer and a PTC material layer. The firstelectrically conductive layer is disposed on a first surface of the PTCmaterial layer, and the second electrically conductive layer is disposedon a second surface of the PTC material layer. The second surface isopposite to the first surface. The first insulating layer is disposed onthe first electrically conductive layer, and the second insulating layeris disposed on the second electrically conductive layer. The firstelectrode layer is disposed on the first insulating layer andelectrically connects to the first electrically conductive layer. Thesecond electrode layer is disposed on the second insulating layer andelectrically connects to the second electrically conductive layer.Corners of the current and temperature sensing element are provided withinsulating members.

In an embodiment, the insulating member extends over a laminate of thefirst electrically conductive layer, the PTC material layer and thesecond electrically conductive layer.

In an embodiment, the first and second electrode layers serve as solderattach surfaces for soldering the PTC device onto a circuit board.

In an embodiment, the insulating member comprises prepreg or resin.

In an embodiment, the insulating member has a hardness larger than thatof the PTC material layer.

In an embodiment, the insulating layer has a glass transitiontemperature (Tg) higher than that of the PTC material layer by at least50° C.

In an embodiment, the first electrode layer, the first insulating layer,the first electrically conductive layer, the PTC material layer, thesecond electrically conductive layer, the second insulating layer andthe second electrode layer are laminated in order.

In an embodiment, the first electrode layer, the first insulating layer,the first electrically conductive layer, the PTC material layer, thesecond electrically conductive layer, the second insulating layer andthe second electrode layer form a bottom surface facing the circuitboard as an interface for soldering onto the circuit board.

In an embodiment, the PTC device further comprises a first electricallyconductive hole and a second electrically conductive hole. The firstelectrically conductive hole penetrates through the first insulatinglayer and connects to the first electrode layer and the firstelectrically conductive layer. The second electrically conductive holepenetrates through the second insulating layer and connects to thesecond electrode layer and the second electrically conductive layer.

In an embodiment, the first electrically conductive hole is located at acenter or a lateral surface of the first insulating layer, and thesecond electrically conductive hole is located at a center or a lateralsurface of the second insulating layer.

In an embodiment, the first insulating layer, the first electricallyconductive layer, the PTC material layer, the second electricallyconductive layer and the second insulating layer form a bottom surfacefacing the circuit board. The first electrode layer retracts at edgesrelative to the first insulating layer to form notches, and the secondelectrode layer retracts at edges relative to the second insulatinglayer to form notches.

In an embodiment, the first electrode layer comprises a bulge extendingto an edge of the first insulating layer, and the second electrode layercomprises another bulge extending to an edge of the second insulatinglayer.

In a printed circuit board (PCB) process, the substrate for making thecurrent and temperature sensing element is drilled to form holes. Theholes are filled with resin or prepreg in a sequential press process toform insulating members. The insulating members are formed at thecorners of the current and temperature sensing element to avoid ordiminish burrs after cutting, and thereby improving tape, reel andsoldering processes.

In the present application, the PTC device in which the first electrodelayer and the second electrode layer at two ends of the laminate serveas solder attach surfaces for soldering onto a circuit board is suitableto be made in small sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application will be described according to the appendeddrawings in which:

FIGS. 1 through 5 show a manufacturing process of a PTC device inaccordance with an embodiment of the present application;

FIG. 6 shows a PTC device in accordance with an embodiment of thepresent application;

FIG. 7 shows a cross-sectional view of a PTC device applied to a circuitboard in accordance with an embodiment of the present application;

FIG. 8 shows a PTC device in accordance with another embodiment of thepresent application;

FIG. 9 shows a way of making a PTC device in accordance with anembodiment of the present application;

FIG. 10 shows a PTC device in accordance with yet another embodiment ofthe present application;

FIG. 11 shows a way of making a PTC device in accordance with anotherembodiment of the present application; and

FIG. 12 shows a PTC device in accordance with an embodiment of thepresent application.

DETAILED DESCRIPTION OF THE INVENTION

The making and using of the presently preferred illustrative embodimentsare discussed in detail below. It should be appreciated, however, thatthe present application provides many applicable inventive concepts thatcan be embodied in a wide variety of specific contexts. The specificillustrative embodiments discussed are merely illustrative of specificways to make and use the invention, and do not limit the scope of theinvention.

Referring to FIG. 1, a composite substrate including a firstelectrically conductive layer 13, a PTC material layer 12 and a secondconductive layer 14 is provided and the composite substrate is drilledto form holes 31 with certain intervals therebetween. Referring to FIG.2, a first electrode layer 17, a first insulating layer 15, the firstelectrically conductive layer 13, the PTC material layer 12, the secondelectrically conductive layer 14, a second insulating layer 16 and asecond electrode layer 18 are pressed to form a laminated structure. Thefirst electrically conductive layer 13 is disposed on a first surface ofa PTC material layer 12, and the second electrically conductive layer 14is disposed on a second surface of the PTC material layer 12. The secondsurface is opposite to the first surface. The first insulating layer 15is disposed on the first electrically conductive layer 13, and thesecond insulating layer 16 is disposed on the second electricallyconductive layer 14. The first electrode layer 17 is disposed on thefirst insulating layer 15, and the second electrode layer 18 is disposedon the second insulating layer 16. The first and second electricallyconductive layers 13 and 14 may be copper layers. The first and secondinsulating layers 15 and 16 may comprise prepreg. The first and secondelectrode layers 17 and 18 may comprise copper. Prepreg is flowable andtherefore can be filled in the holes 31 during pressing to forminsulating members 30. Alternatively, the holes 31 can be filled withmaterial such as resin before pressing to form the insulating members30. The material of the insulating members 30 is not limited to prepregor resin, other polymers with required features such as insulation andhardness can be used instead.

The PTC material layer 12 comprises crystalline polymer and conductivefiller dispersed therein. The crystalline polymer comprisespolyethylene, polypropylene, polyvinyl fluoride, mixture or copolymerthereof. The conductive filler may comprise carbon-containing filler,metal filler, and/or ceramic filler. For example, the metal filler maybe nickel, cobalt, copper, iron, tin, lead, silver, gold, platinum, orthe alloy thereof. The ceramic filler may be titanium carbide (TiC),tungsten carbide (WC), vanadium carbide (VC), zirconium carbide (ZrC),niobium carbide (NbC), tantalum carbide (TaC), molybdenum carbide (MoC),hafnium carbide (HfC), titanium boride (TiB₂), vanadium boride (VB₂),zirconium boride (ZrB₂), niobium boride (NbB₂), molybdenum boride(MoB₂), hafnium boride (HfB₂), or zirconium nitride (ZrN). Moreover, theconductive filler may be the mixture, alloy, solid solution orcore-shell of the aforesaid metal and ceramic fillers.

Referring to FIGS. 3 and 4, FIG. 3 is a side view of the laminatedstructure and FIG. 4 is a top view thereof. Holes 20 with certainintervals are made in the laminated substrate. As shown in FIG. 4, thehole 20 is located among adjacent four insulating members 30. Verticaland horizontal dashed lines are predetermined cutting lines and theinsulating members 30 are located at intersections of the vertical andhorizontal cutting lines. Upper holes 20 go through the first electrodelayer 17 and the first insulating layer 15 and stop at the firstelectrically conductive layer 13. Lower holes 20 go through the secondelectrode layer 18 and the second insulating layer 16 and stop at thesecond electrically conductive layer 14. The holes 20 may be directlymade by laser drilling which is suitable for small size holes and cancontrol the drilling depth precisely. Alternatively, the first electrodelayer 17 and the second electrode layer 18 can be etched first andfollowed by laser drilling the first insulating layer 15 and the secondinsulating layer 16. The holes 20 may be made by mechanical drilling.However, the first electrically conductive layer 13 and the secondelectrically conductive layer 14 may be partially and fully removed bymechanical drilling.

Referring to FIG. 5, the upper and lower holes 20 are filled withelectrically conductive material to form first electrically conductivemembers 21 and second electrically conductive members 22. In anembodiment, the first and second electrically conductive members 21 and22 may be made by electroplating copper. During electroplating, coppermay be electroplated onto the first electrode layer 17 and the secondelectrode layer 18 also to increase their thicknesses. In case of largeholes 20, the material of the first and second electrically conductivemembers 21 and 22 may be not able to fully fill the holes 20. As aresult, recesses may be generated on the surfaces of the conductivemembers 21 and 22. The first and second electrode layers 17 and 18 maybe plated with tin to enhance solderability. Afterwards, the laminatedstructure is divided along the cutting lines to form a plurality of PTCdevices 10. A single PTC device 10 is shown in FIG. 6. In an embodiment,the PTC device 10 has equal width and thickness, that is, as shown inFIG. 6, the first electrode layers 17 and 18 are square. As such, thePTC device 10 is not affected even if it rolls over. It should be notedthat the first and second electrode layers 17 and 18 are not limited tosquare and may be rectangular. The insulating members 30 are formed atcorners of the middle of the PTC device 10. The material of theinsulating members 30 such as prepreg or resin is tougher than the PTCmaterial layer 12 and, unlike the first electrically conductive layerand the second electrically conductive layer, it has no metal ductility.Therefore, the insulating members 30 can protect the PTC material andavoid occurrence of burr or flash. To prevent the PTC material layer 12from generating burr or flash, a hardness of the insulating member 30 islarger than that of the PTC material layer 12 or a glass transitiontemperature (Tg) of the insulating member 30 is higher than that of thePTC material layer 12 by at least 50° C.

FIG. 7 shows the PTC device 10 soldered onto a circuit board 60 inaccordance with an embodiment of the present application. The PTC device10 is soldered onto the circuit board 60 through solder paste 61. ThePTC device 10 comprises a current and temperature sensing element 11,the first insulating layer 15, the second insulating layer 16, the firstelectrode layer 17, the second electrode layer 18, the firstelectrically conductive member 21 and the second electrically conductivemember 22. The current and temperature sensing element 11 is a laminatecomprising a first electrically conductive layer 13, a secondelectrically conductive layer 14 and a PTC material layer 12 laminatedtherebetween. The insulating members 30 extend over the laminate of thefirst electrically conductive layer 13, the second electricallyconductive layer 14 and the PTC material layer 12. More specifically,four insulating members 30 are formed at corners of the current andtemperature sensing element 11. Each corner connects adjacent lateralsurfaces of the current and temperature sensing element 11. The firstelectrode layer 17 is disposed on the first insulating layer 15, andelectrically connects to the first electrically conductive layer 13. Thesecond electrode layer 18 is disposed on the second insulating layer 16,and electrically connects to the second electrically conductive layer14. The first electrically conductive member 21 penetrates through thefirst insulating layer 15 and connects to the first electrode layer 17and the first electrically conductive layer 13. The second electricallyconductive member 22 penetrates through the second insulating layer 16and connects to the second electrode layer 18 and the secondelectrically conductive layer 14. In this embodiment, the firstelectrode layer 17, the first insulating layer 15, the firstelectrically conductive layer 13, the PTC material layer 12, the secondelectrically conductive layer 14, the second insulating layer 16 and thesecond electrode layer 18 are stacked in order and form a bottom surface24. The bottom surface 24 faces the circuit board 60 as an interface forsoldering onto the circuit board 60. During soldering, solder paste 61climbs up along the first electrode layer 17 and the second electrodelayer 18. In other words, the first electrode layer 17 and the secondelectrode layer 18 serve as solder attach surfaces when soldering thePTC device 10 onto the circuit board 60.

When cutting to form the PTC devices 10, as shown in FIG. 5, the bottomsecond electrode layer 18 may be stretched by the cutter to cause burrsbecause of metal ductility. FIG. 8 shows a PTC device 70 in accordancewith another embodiment of the present application. In comparison withthe PTC device 10 shown in FIG. 6, The first electrode layer 17 retractsat edges relative to the first insulating layer 15 to form notches 26,and the second electrode layer 18 retracts at edges relative to thesecond insulating layer 16 to form notches 26 as well. In thisembodiment, the PTC device 70 is symmetrical. FIG. 9 shows a way ofmaking the first and second electrode layers 17 and 18 of the PTC device70. Before cutting, grooves 81 are made in the first and secondelectrode layers 17 and 18. The grooves 81 surround the holes 20 andlocate at cutting positions. The intersections of vertical andhorizontal grooves 81 correspond to the positions of the insulatingmembers 30. The width of the groove 81 is larger than cutting width andis approximately the width of a cutter plus twice the width of the notch26. As a result, the cutter does not touch the first and secondelectrode layers 17 and 18 when cutting to form the notches 26, so as toavoid burrs on the electrode layer 17 or 18.

FIG. 10 shows a PTC device 90 in accordance with yet another embodimentof the present application. The first and second electrode layers 17 and18 of both the PTC device 90 and the PTC device 70 retract their edges.Different from the PTC device 70, the edges of the first electrode layer17 of the PTC device 90 comprise bulges 27 extending to the edges of thefirst insulating layer 15, and the edges of the second electrode layer18 of the PTC device 90 comprise bulges 28 extending to the edges of thesecond insulating layer 16. One of the bulges 27 and one of the bulges28 reach the bottom of the PTC device 90 to provide paths for solderattachment or solder climbing. As such, it is advantageous to enhancesolder attachment especially for large notches 26. FIG. 11 shows a wayof making the first and second electrode layers 17 and 18 of the PTCdevice 90. Grooves 91 are made in the first and second electrode layers17 and 18. The grooves 91 correspond to cutting positions but are notcontinuous. The first and second electrode layers 17 and 18 ofneighboring devices 90 are partially connected. The connection of thefirst and second electrode layers 17 and 18 form the bulges 27 and 28.In an embodiment, the width of the bulge 27 or 28 is 20-60% of the widthof the first or second insulating layer 15 or 16. The width of thegroove 91 is larger than cutting width, and is approximately equal tothe width of a cutter plus twice the width of the notch 26. Because thebulges 27 and 28 are relatively small in comparison with the first andsecond electrode layers 17 and 18, the burr issue can be diminished whencutting the bulges 27 and 28 and solder attachment becomes moreeffective.

The electrically conductive member 21 or 22 may be located at but notlimited to the center of the insulating layer 15 or 16. Alternatively,the electrically conductive members 21 and 22 may be located at centerportions of lateral surfaces of the device as long as they canelectrically connect the first electrically conductive layer 13 and thefirst electrode layer 17 and electrically connect the secondelectrically conductive layer 14 and the second electrode layer 18. Inthe above embodiments, the insulating layers 30 of prepreg or resinincrease structural strength to be suitable for device miniaturization.

FIG. 12 shows a PTC device of the present application, which is similarto the device disclosed in U.S. Pat. No. 6,377,467 except insulatingmembers are formed at corners of the device to reduce burrs. A PTCdevice 40 comprises a current and temperature sensing element 41, afirst insulating layer 45, a second insulating layer 46, a firstelectrode layer 47 and a second electrode layer 48. The current andtemperature sensing element 41 is a laminated structure comprising afirst electrically conductive layer 43, a second electrically conductivelayer 44 and a PTC material layer 42. The first electrically conductivelayer 43 is disposed on a first surface of the PTC material layer 42.The second electrically conductive layer 44 is disposed on a secondsurface of the PTC material layer 42. The second surface is opposite tothe first surface. The first insulating layer 45 is disposed on thefirst electrically conductive layer 43, and the second insulating layer46 is disposed on the second electrically conductive layer 44. The firstelectrode layer 47 has two sections disposed on the first insulatinglayer 45 and the second insulating layer 46, respectively, andelectrically connects to the first electrically conductive layer 43through a conductive hole 49. The second electrode layer 48 has twosections disposed on the first insulating layer 45 and the secondinsulating layer 46, respectively, and electrically connects to thesecond electrically conductive layer 44 through a conductive hole 50.Insulating members 51 are formed at four corners of the current andtemperature sensing element 41 of the PTC device 40. The material of theinsulating members 51 such as prepreg or resin is tougher than the PTCmaterial layer 42 and do not have metal ductility which is inherent inthe first electrically conductive layer 43 and the second electricallyconductive layer 44. The insulating members 51 can protect the PTCmaterial and avoid occurrence of burr or flash.

In addition to over-current protection applications, the PTC device ofthe present application can conduct temperature sensing. Insulatingmembers formed at corners of the current and temperature sensing elementcan effectively resolve burr problems and improve sequential tape, reeland soldering processes. The PTC device is made of a laminated structurethrough pressing and cutting, a surface composed of laminated layersserves as a bottom surface for soldering. Not only are the simplestructure and manufacturing process, but also it is suitable to be madefor small devices such as form factors 0402 and 0201. In an embodiment,the PTC device has the same width and thickness to exclude the influencecaused by rollover.

The above-described embodiments of the present invention are intended tobe illustrative only. Numerous alternative embodiments may be devised bypersons skilled in the art without departing from the scope of thefollowing claims.

1. A PTC device, comprising: a current and temperature sensing elementbeing a laminated structure of a first electrically conductive layer, asecond electrically conductive layer and a PTC material layer, the firstelectrically conductive layer being disposed on a first surface of thePTC material layer, the second electrically conductive layer beingdisposed on a second surface of the PTC material layer, the secondsurface being opposite to the first surface; a first insulating layerdisposed on the first electrically conductive layer; a second insulatinglayer disposed on the second electrically conductive layer; a firstelectrode layer disposed on the first insulating layer and electricallyconnecting to the first electrically conductive layer; a secondelectrode layer disposed on the second insulating layer and electricallyconnecting to the second electrically conductive layer; wherein cornersof the current and temperature sensing element are provided withinsulating members, wherein the first insulating layer, the firstelectrically conductive layer, the PTC material layer, the secondelectrically conductive layer and the second insulating layer form abottom surface facing a circuit board, the first electrode layerretracts at edges relative to the first insulating layer to formnotches, and the second electrode layer retracts at edges relative tothe second insulating layer to form notches, wherein the first electrodelayer comprises a bulge extending to an edge of the first insulatinglayer, and the second electrode layer comprises another bulge extendingto an edge of the second insulating layer.
 2. The PTC device of claim 1,wherein the insulating member extends over the first electricallyconductive layer, the PTC material layer and the second electricallyconductive layer.
 3. The PTC device of claim 1, wherein the first andsecond electrode layers serve as solder attach surfaces for solderingthe PTC device onto the circuit board.
 4. The PTC device of claim 1,wherein the insulating member comprises prepreg or resin.
 5. The PTCdevice of claim 1, wherein the insulating member has a hardness largerthan that of the PTC material layer.
 6. The PTC device of claim 1,wherein the insulating member has a glass transition temperature higherthan that of the PTC material layer by at least 50° C.
 7. The PTC deviceof claim 1, wherein the first electrode layer, the first insulatinglayer, the first electrically conductive layer, the PTC material layer,the second electrically conductive layer, the second insulating layerand the second electrode layer are laminated in order.
 8. The PTC deviceof claim 1, wherein the first electrode layer, the first insulatinglayer, the first electrically conductive layer, the PTC material layer,the second electrically conductive layer, the second insulating layerand the second electrode layer form a bottom surface facing the circuitboard as an interface for soldering onto the circuit board.
 9. The PTCdevice of claim 1, further comprising: a first electrically conductivehole penetrating through the first insulating layer and connecting tothe first electrode layer and the first electrically conductive layer;and a second electrically conductive hole penetrating through the secondinsulating layer and connecting to the second electrode layer and thesecond electrically conductive layer.
 10. The PTC device of claim 9,wherein the first electrically conductive hole is located at a center ora lateral surface of the first insulating layer, and the secondelectrically conductive hole is located at a center or a lateral surfaceof the second insulating layer.
 11. (canceled)
 12. (canceled)